The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
During premixed charge compression-ignition (PCCI) engine operation, auto-ignited combustion depends on the cylinder charge temperature, charge composition, and cylinder pressure at intake valve closing. Hence, the control inputs to the engine, such as amount of fuel, fuel injection timing, EGR valve open position, and intake and exhaust valve profiles, must be coordinated to ensure that those key cylinder variables are within a range where the auto-ignited combustion can be efficiently achieved. Among those inputs, the amount of residual gas available to the engine and the start of the fuel injection timing are important. The amount of residual gas available is a slow response parameter making transient conditions difficult to control without excess audible combustion noise and torque output irregularities.
During PCCI combustion, control of the variables is determined from steady-state engine calibrations. When steady-state engine operation is interrupted, such as during a requested torque transient or combustion mode transition, the engine is controlled to a new steady-state calibration at the requested operating state as determined from the new operator torque request. This type of control fails to comprehend that the engine actuators and associated control parameters can have different reaction times, with residual gas mass response among the slowest. At small torque and combustion mode transitions, the reaction times are close enough to each other that torque disturbances and audible combustion noise are minimized. At large transients, the reaction times cannot match the rate of change, resulting in a loss of combustion control until the engine actuators and associated control parameters reaction times are able to respond. The period of loss of control results in torque disturbances and audible combustion noise. When the loss of control occurs, this also results in emission spikes as the combustion process is no longer operating within operational parameters.